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WO2006036330A2 - Synthese numerique de signaux de communication - Google Patents

Synthese numerique de signaux de communication Download PDF

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Publication number
WO2006036330A2
WO2006036330A2 PCT/US2005/028798 US2005028798W WO2006036330A2 WO 2006036330 A2 WO2006036330 A2 WO 2006036330A2 US 2005028798 W US2005028798 W US 2005028798W WO 2006036330 A2 WO2006036330 A2 WO 2006036330A2
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WIPO (PCT)
Prior art keywords
communication
pulse
waveform
signals
signal
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WO2006036330A3 (fr
Inventor
John Santhoff
Steven A. Moore
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Pulse Link Inc
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Pulse Link Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/7163—Spread spectrum techniques using impulse radio
    • H04B1/7176—Data mapping, e.g. modulation

Definitions

  • Modulating a carrier wave with a baseband, or information, signal has been the basis of conventional RF communications since the advent of continuous wave trarisrnilters. Each information channel uses a different carrier wave spaced far enough away in frequency from adjacent carriers to avoid interference. Under this approach, a single information channel thus modulates a single carrier wave.
  • a general solution to increase data rates is to employ 'Multiplexing" techniques, such as frequency division multiplexing (FDM). Ratherthanpuslihgaclatastream through into blocks and modulate some fixed number of blocks in parallel, putting each onto separate "sub-carrier" waves at slower transmission rates. The modulated subcamers are subsequently summed into a composite waveform or signal and transmitted Uponreception, the composite signal is broken back down to its component subcarrier frequencies from which tie data are extracted.
  • FDM requires, however, that the subcarrier frequencies be spaced far enough apart to prevent interference, leading to comparative inefficiencies in frequency use.
  • orthogonal frequency division multiplexing OFDM
  • orthogonal means that the modulated carriers essentially do not interfere with each other, but are yet closely packed together in frequency. Closely packing Hie multiple subcarrier frequencies results in an important efficiency gain because the radio frequency occupied by the OFDM signal is minimized
  • OFDM requires a method to generate each of the orthogonal subcarrier frequencies.
  • a separate oscillator was used to produce each subcarrier wave, but the oscillatoishadtobecareMysynchionizedto ensure proper coherence between the subcarriers in the final composite waveform, adding significant complexity and cost to the OFDM system.
  • a later approach provided a significant improvement by eliminating the need for a bank of synchronized, separate oscillators, using instead a digital signal processing (DSP) module.
  • DSP digital signal processing
  • an input data, stream of binary digits, or "bit stream” is mapped into a sequence of code symbols that is subjected to an inverse fast fourier transform (inverse FFT, or IFFT) in the DSP module.
  • inverse FFT inverse fast fourier transform
  • the IFFT produces a sequence of orthogonal time domain signals (i.e., the orthogonal subcaniers for the OFDM signal).
  • This method generates Ihe orthogonal subcaniers numerically by usingadedicatedconputingmodule, insteadofabarikofsyncrironciedoscillatois.
  • the radio fiequency band of the subcaniers generated by the IFFT process are fixed according to a "width" of the IFFT and the sampling rate of the DSP, which are both limited by hardware and software designs.
  • a basic computational requirement of the M 1 T algorithm is tot the length of the data sequence on ⁇ vhichihe orjei ⁇ onisperformedmustgeneraUybesomenu ⁇ 1024, or2048, thereby limiting flexibility.
  • the orthogonal subcaniers must then be summed, but the resulting composite signal still requires low-pass filtering and ur ⁇ xaweisionus ⁇ ig a lo ⁇ oscillator to the radio fiequency used for taismissi ⁇ rx
  • the present invention provides apparatus, systems and methods to simplify communication devices, while achieving high datarates.
  • One embodiment of the present invention replaces the IFFT, the low pass filter, and the up-conversioii step that requires a local oscillator, with a digital processor and a single high-speed digital-to-analog converter (DAQ.
  • DAQ digital-to-analog converter
  • This embodiment of the present invention synthesizes, or generates communication signals directly, ⁇ vhich can then be transmitted, without "up-conversiori' to the transmission fiequency, and without many of the processing steps used in conventional communication devices.
  • one embodiment of flie present invention comprises a digital processor configured to encode data ontooneormorei ⁇ presentativetransmissionsymbols.
  • Awaveformgenerator such assabigh-speedDAC,is configured to generate a waveform fiom the encoded representative transmission symbols. This waveform is then passed to an antenna and transmitted.
  • communication signals can be generated directly at their transmission fiequency, including ttansmission frequencies of 5 gigahertz and above.
  • Another feature of the present invention is that in one embodiment, only one DAC is required, as its high speed allows it to generate multiple communication signals at different fiequencies, thereby eliminating Ihe need for many components, such as multiple field-prograrnrnable-gate-arrays (FPGAs) found in ODnventiondcommunicatio ⁇ i devices.
  • FPGAs field-prograrnrnable-gate-arrays
  • PIG. 1 illustrates aconventionalmelhodoforthogonalfiequency divisionmultiplexing
  • FIG. 2 illustrates an orthogonal fequency division multiplexing method constructed according to one embodiment of the present invention
  • FIG. 3 illustrates a method to synthesize virtually any waveform according to anoflier embodiment of the present invention
  • FIG.5 illustrates two ultra-wideband pulses
  • FIG.6 illustrates a 16-point quadrature amplitude modulation "constellation
  • FIG.7 illustrates the data transformations for orthogonal frequency division multiplexing performed by another embodiment of the present invention
  • FIG.8 illustrates aportionof adgital-to-analog ⁇ nvertert ⁇ candirec ⁇ consistentwith one embodiment of the present invention
  • FIG. 11 fflustratesr»rtior ⁇ ofaiulta-wideban ⁇
  • FIG. 12 fflustratesar»rtion of acombhed signal ⁇ 11.
  • the present invention provides apparatus, systems and methods for directly digitally synthesizing communication signals or waveforms. That is, waveforms that carry data are generated by a digital-to-analog converter (DAQattheradofecpencyusedtotrarm ⁇ te This contrasts with cxmve ⁇ tionalcc)mm ⁇ a ⁇ ic ⁇ onmethods that generate the waveforms at one frequency and transmit them at another frequency.
  • DAQattheradofecpencyusedtotrarm ⁇ te This contrasts with cxmve ⁇ tionalcc)mm ⁇ a ⁇ ic ⁇ onmethods that generate the waveforms at one frequency and transmit them at another frequency.
  • the present invention can generate waveforms having a transmission radio frequency that may range from 5 megahertz (MHz)toat Ieast5 gigahertz (GHz), withHgherfreqpendes,suchas 10 GHz andhigher also obtainable.
  • the communication signals, or waveforms may be in the form of electromagnetic waves, discrete eledromagneticpulseSjWaveletsorothertjpesofcommuriic ⁇ onsignals.
  • One embodiment of the present invention provides a method for performing frequency division multiplexing (FDM).
  • FDM frequency division multiplexing
  • This embodiment directly synthesizes the modulated, digital time domain waveforms that comprise the subcarriers.
  • Information desired for transmission may be modulated, or encoded onto each subcanier, which prior to synthesis is represented as a group of numerical values.
  • a waveform generator such as a digital-to- analog converter (DAQ)
  • DAQ digital-to- analog converter
  • the subcanier waveforms may be constructed to possess any desired characteristic.
  • a high-speed DAC takes the numerical values that represent the subcanier waveforms and converts the numbers to an analog waveform for transmission through a communication channel, which may be air, space, water, wire, cable, optical fiber, or other ⁇ nmunication channels.
  • Another 1 embodiment of the present invention provides mutually oilhogonal synthesized subcanier waveforms ⁇ thereby creating orthogonal frequency division multiplexing (OFDM) waveforms.
  • OFDM orthogonal frequency division multiplexing
  • One version of this embodiment creates the OFDM waveforms at the radio frequency used for transmission. That is, the synthesized waveforms do not require up-conversion to the cxmimunication channel frequency.
  • aDAC with a sampling rate of 20 gjga samples per second may employed, allowing frequency content up to 10 GHz to be accurately represented in the transmitted waveform.
  • DACs with slower, or faster sampling rates may be employed, depending upon the desired transmission frequency.
  • One method for modulating the information onto the subcarriers comprises quadrature amplitude modulation (QAM), but other modulation (Le., encoding) methods, such as the various forms of phase shift keying (PSK) or differential phase shift keying (DPSK), maybe employed in other embodiments.
  • QAM quadrature amplitude modulation
  • PSK phase shift keying
  • DPSK differential phase shift keying
  • the portion of the radio frequency spectrum (i.e., the radio frequency band) occupied by the orthogonal subcarriers may conform to the specifications of existing, deployed OFDM systems.
  • the IFFT process is no longer required, data processing is not limited to the 2 ⁇ data sequence length of conventional OFDM systems (discussed is the Background of the Invention), thereby increasing efficiency, and increasing system flexibility.
  • the present invention can directly replace older OFDM transceivers, and enable new OFDM system designs. Ih addition, the present invention reduces the number of components requited to build a tratisc ⁇ ver, therebyreducmgmam Referring to EIG.
  • step 110 the data bit stream is routed to a digital processor, which may be a digital signal processor, Si step 120, the digital signal processor partitions tiie data bit stream into blocks orbit-words of apre ⁇ letermined length.
  • a fixed number of bit-words determined by design limits, are used to form a sequence ofbit-words.
  • step 140 tiie sequence ofbit-words are then converted or "mapped" into transmission symbols using techniques such as phase shift keying (PSK) or differential phase shift keying (DPSK), creating a sequence of transmission symbols.
  • PSK phase shift keying
  • DPSK differential phase shift keying
  • step 150 the sequence of transmission symbols is then converted by an inverse digital fourier transform (inverse DFI), or an IFFT process.
  • inverse DFI inverse digital fourier transform
  • the product of tiie IFFT process is a sequence of complex values, each representing a fiequency and phase in the time domain.
  • the fiequencies generated by the IFFl process constitute the OFDM subcarriers because they are mutually orthogonal due to the orthogonal characteristics of the IFFT process.
  • Each specific fiequency is a function of tiie system sampling rate and the "width" of the IFFT (i.e., 2 ⁇ for some N).
  • Information, or data is represented in an individual subcarrier waveform according to tiie method that was used to map tiie data into transmission symbols in step
  • step 160 the output of the IbFl ' is ftien routed through a shaping filter, followed by a low pass filter, in step 170.
  • Si step 185 flie filtered waveform is then "up-converted" to flie radio frequency used for transmission (i.e., flie carrier fiequency, fit), which requires mixing with a sinusoidal waveform e ja>ct (in step 180), which is generated by a local oscillator.
  • step 190 fheresultingmodulatedwavefomiisth&i ⁇
  • HG. 2 illustrates one embodiment of the present invention that generates OFDM communication waveforms precisely at the radio frequency used for transmission.
  • a data bit stream of interest such as voice, video, audio, or Internet content is obtained
  • Ih step 210 the data bit stream is passed to the processor.
  • the processor may comprise one or more discrete components, and may include a finite state machine, a digital signal processor, and/or computer logic steps stored inmemory or built into digital hardware. It will be appreciated that other components may comprise theprocessor.
  • bit stream is partitioned into bit-words, or groups ofb ⁇ s.
  • the length of each bit-word depends primarily upon the modulation method selected.
  • a desired number of bit-words are then used to form a sequence ofbit-words.
  • each bit-word in the sequence is then converted or ' 'mapped' ' into a transmission or data symbol, resulting in a sequence of transmission symbols tiiatnowincludetheOFDMmodulation.
  • step 250 the transmission symbols areusedto modulate, or enc ⁇ iesubcamerwavefomisihat are represented as numerical values. That is, the encoding of data onto the representation of communication waveforms is performed digitally by algorithms that generate numerical values representing tiie now encoded communication waveforms.
  • step 260 the modulated "time domain" subcarrier waveforms ate summed, resulting in a digitized, or ' 'sampled,' ' version of the final teansmission waveform
  • step 270 this digital sequence is passed to the digital-to-analog converter PAQ for conversion to an analog waveform that is then transmitted in step 190.
  • the transmission step 190 may employ one or more antennas, amplifiers and/or falters to facilitate transmission over the cornmunicarion channel of interest, and/or other components necessary to accomplish signal transmission at the chosen radio frequency and through the chosen commumcationmediurn.
  • One feature of the present invention is that the now modulated time domain communication waveforms are synthesized, or created at the radio fiequencies used for transmission
  • the shaping filter (step 160), low pass filter (step 170), oscillator (step 180) and mixer, or up-converter (step 185), all required ii conventional OEDM systems, are eliminated This reduces manufacturing cost, and subsequentretail cost, asweUasreducingproductsizeandpow ⁇ requirements.
  • the entire IFFT process is eliminated, resulting in greaterprocessmg flexibility becan ⁇
  • FIG.3 another embodiment of the rjresentmve ⁇ don is illustrated. Si this embodiment, any type of waveform, or modulated waveform maybe generated.
  • the present invention can directly synthesize any desired communication signal, that may be modulated by any known, or yet to be developed, modulation method.
  • the ⁇ sent invention can employ amplitude modulation, phase modulation, frequency modulation, quadrature amplitude modulation, pulse-code modulation, pulse-width modulation, pulse-amplitude modulation, pulse-position modulation, frequency-shift keying, phase-shift keying, and any other type of modulation method.
  • the present invention can directly generate discrete electromagnetic pulses, rather than ftie substantially continuous sinusoidal waveforms used in conventional communication systems.
  • One communication technologyfhat in some embodiments, employs discrete electromagnetic pulses is known as "ultra-wideband.”
  • UWB ultra-wideband
  • UWB pulses may be transmitted without modulation onto a sine wave, or a sinusoidal carrier, in contrast with conventional carrier wave communication technology, such as a conventional OFDM communication technology, as described above.
  • UWB generally requires neither an assigned frequency nor apow ⁇ amplifier.
  • UWB may be achieved by mixing baseband pulses (Le., information- ⁇ rrying pulses), with a carrier wave Ihat controls a center frequency of aresultingsignaL
  • the resulting signal is then transmitted using discretepulses of electromagnetic energy, as opposed to transmitting a substantially continuous sinusoidal signal.
  • IKKK 802.11a is a wireless local area network (LAN) protocol, which transmits a sinusoidal radio frequency signal at a 5 GHz center frequency, with aradio frequency spread of about 5 MHz.
  • LAN local area network
  • a carrier wave is an electromagnetic wave of a specified frequency and amplitude that is emitted by a radio transmitter in order to carry information
  • the 802.11 protocol is an example of a carrier wave communication technology.
  • the carrier wave comprises a substantially continuous sinusoidal wavefomi having a specific nanow radio frequency (5 MHz) that has a duration 1hat may range from seconds to minutes.
  • an ultra-wideband (UWB) pulse may have a 2.0 GHz center fiequency, wifli a fequency spread of approximately 4 GHz, as shown in ElG. 5, which illustrates two typical UWB pulses.
  • FIG.5 illustrates that the shorter the UWB pulse in time, the broader the spread of its frequency spectrum This is because bandwidth is inversely proportional to the time duration of Hie pulse.
  • a 60Q-picosecond UWB pulse can have about a 1.8 GHz center frequency, with a frequency spread of approximatery 1.6 GHz and a 300-picosecond UWB pulse can have about a 3
  • UWB pulses generally do not operate within a specific frequency, as shown in FIG. 4.
  • Ether of the pulses shown in FIG. 5 may be frequency shifted, tor example, by using heterodyning, to have essentially the same bandwidth but r ⁇ tered at any desired frequency.
  • UWB pulses are spiead across an extremely wide frequency range, UWB communication systems allow communications at very high data rates, such as 100 megabits per second or greater.
  • UWB pulses are spread across an extremely wide frequency range, Ihepow ⁇ sampled in, tor example, a one megahertz bandwidth, is very low.
  • UWB pulses of one nano-second duration and one milliwatt average power (0 dBm) spreads the power over the entire one gigahertz frequency band occupied by the pulse.
  • the resulting power density is thus 1 milliwatt divided by the 1,000 MHz pulse bandwidth, or 0.001 milliwatt per megahertz (-30 dBm/MHz).
  • UWB pulses may be transmitted at relatively low power density (milliwatts per megahertz).
  • an alternative UWB communication system may transmit at a higher power density.
  • UWB pulses may be transmitted in a range between 30 dBm to -50 dBm
  • UWB pulses may also be transmitted through wire, cables, fiber-optic cables, and UWB pulses transmitted flTroughmany wiremedkwiUnotinterlerewithwirelessradio frequencytransrnissions. Therefore, the power (sampled at a single frequency) of UWB pulses transmitted though wire media may range from about +30 dBm to about -140 dBm.
  • Fractional bandwidth is defined as 2 times the difference between the high and low 10 dB cutoff frequencies dividedby the sum of the high and low 10 dB cutoff frequencies.
  • fractional bandwidfti is the percentage of a signal's center frequency that the signal occupies.
  • IhatiS j UWB as defined by ⁇ iepresentinve ⁇ ti ⁇ i is not necessarily limited to the current FCC definition. As discussed above, some types ofUWB are a form of impulse communications, and some embodiments may not fit within the current FCC definition.
  • UWB communication methods may transmit UWB pulses that occupy 500 JVIHz bands within the 7.5 GHz FCC allocation (from 3.1 GHz to 10.6 GHz).
  • UWB pulses have about a 2-nanosecond duration, which corresponds to about a 500 MHz bandwidth.
  • the center frequency of the UWB pulses can be varied to place them wherever desired within the 7.5 GHz allocation.
  • an Inverse Fast Fourier Transform EFFT is performed on parallel data to produce 122 carriers, each approximately 4.125 MHz wide.
  • Ii this embodiment also known as Orthogonal Frequency Division Multiplexing (OFDM)
  • OFDM Orthogonal Frequency Division Multiplexing
  • the resultant UWB pulse, or signal is approximately 5O6 MHz wide, and has a 242 nanosecond duration. It meets Ihe current FCC rules for UWB communications because it is an aggregation of manyrelativelynarrOwband carriers rather thanbecause of the duration of eachpulse.
  • UWB pulse durations may vary from 2 nanoseconds, which occupies about 500 MHz, to about 133 picoseconds, which occupies about 7.5 GHz ofbandwidth. That is, a single UWB pulse may occupy substantially all ofthe entire aUccation for communications (fiom3.1 GHzto 10.6 GHz).
  • Yet another UWB communication method being evaluated by the IEEE standards committees comprises transmitting a sequence of pulses that may be ar ⁇ proximately 0.7 ria ⁇ seccmds or less m duration, and at a ch ⁇ approximately 1.4 giga pulses per second.
  • the pulses are modulated using aDirect ⁇ equence modulation technique, and is calledDS-UWB.
  • Operatim ⁇ twobandsisco ⁇ terrplat ⁇ signal, wMettie second band is centerednear 8 GHz, witha2.8 GHz wide UWB signal. Operationmay occur at either or both ofthe UWB bands.
  • Data rates between about 28 Megabits / second to as much as 1320 Megabits/second are contemplated
  • UWB ultra-wideband
  • the present invention may be employed by any ofthe above-described UWB methods, or others yet to be developed
  • data of interest such as voice, video, audio, text, Internet content, or any ottier data of interest
  • the data in the form of binary digits, such as abit stream is passed to the processor.
  • Theprocessor may comprise one ormore discrete components, and may include a finite state machine, a digital signal processor, and/or computer logic steps stored in memory or built into digital hardware. It will be appreciated that other components may comprise the processor.
  • bit stream is partitioned into groups ofbits.
  • the size of each bit group depends primarily upon Hie employed modulation method.
  • each group ofbits is tfien converted or "mapped" into a data symbol, resulting in a sequ ⁇ ice of transmission, or data symbols. That is, the bit groups are changed in numerical value by the modulationmetlTodthat is employed.
  • the now modulated bit groups are combined with a chosen waveform.
  • a waveform representing a sinusoidal canierwave maybe used. That is, the data symbols areusedtomodulate, or encode waveforms that are represented as numerical values.
  • Hie encoding of data onto the representation of communication waveforms is performed digitally by algorithms that generate numerical values representing the now encoded comm ⁇ ni ⁇ on waveforms.
  • step 270 this digital sequence is passed to the digital-to-analog converter (DAC) for conversion to an analog waveform that is then transmitted in step 190.
  • DAC digital-to-analog converter
  • Hie transmission step 190 may employ one or more antennas, amplifiers and/or filters to fecilitate transmission over the ⁇ rnmunication channel of interest, and/or other components necessary to accomplish signal transmission at the chosen radio frequency and through the chosen commumcationmediurn.
  • One feature of the present invention is ftiat the now modulated time domain communication waveforms are synthesized, or created at tfie radio fiequencies used for transmission
  • Ihe entire IFFT process is eliminated, resulting k greater processing flexibiHty because the 2 ⁇
  • the final analog waveform transmitted in step 190 may be a substantially ⁇ ntinuous sinusoidal waveform having a duration, that may last between milliseconds to minutes and hours, or Hie analog waveform maybe in the form of discrete pulses of electromagnetic energy, used in impulse communications, such as ultra-wideband, and oftier forms of impulse communications.
  • the mapping step 240 (shown in FIG. 2) then comprises mapping each 4-bit word to one of 16 transmission symbols representing specific, unique combinations of amplitude andphase angle.
  • FIG.6 depicts a 16-point QAM mapping "constellation," where eachofthe 16 points 300 represents a transmission symbol comprising a specific amplitude r and phase angle ⁇ . Once all the bit-words are "mapped,” then in synthesis step 250, a digital pulse of a specific duration is generated The digital pulse represents a subcamer waveform as modulated by the amplitude and phase of the QAM transmission symbol
  • mapping 240 and synihesizing 250 are performed for all of the bit-words generated in the bit-word sequence formation step 230.
  • FIG.7 illustrates this sequence ofbit-word ordering by presenting another depiction of the method illustrated in FIG.2.
  • the data bit stream 100 (shown as 1 and -1 bits) is partitioned into 4-bit words, discussed in FIG.2 as steps 220 and230.
  • Nwords comprising a wordsequence, and each word is mapped into the QAM constellation shown rnMG.6,resultmginanewsequenreoftransn]i ⁇ (n ⁇ is drawn fiom the set of 16 points in the constellation (FIG.2, step 240).
  • the samples are summed (FIG.2, step 260) and the resulting summed samples are passed to the high-speed digital-to-analog converter (DAC) 270, that generates a waveform fiorn the summed samples at the desired transmission fiequency, which is then transmitted 190.
  • DAC digital-to-analog converter
  • an 802.11(a) signal 310 is shown with an ultra-wideband pulse 305.
  • the 802.11(a) signal 310 comprises a sinusoidal waveform incorporating either OFDM, direct sequence modulation, or another suitable modulation method
  • the ultra-vvideband pulse 305 comprises a discrete pulse of electromagnetic energy that may inrarporarerrmydifferentmodu ⁇
  • both the 802.1 l(a)signal310andtheul-ra- wideband pulse 305 may be synthesized by the methods disclosed herein to form a combined signal 320.
  • a signal section 300 is shown in both FIGS. 11 and 12, with FIG. 12 showingthe combined signal 320, and both the 802.11(a) signal310 andtheultra-widebandpulse 305.
  • data for each signal may be partitioned into groups, and in step 242 each group of bits is then converted or "mapped" into a data symbol, resulting in a sequence of transmission, or data symbols.
  • Hie now modulated bit groups are combined with chosen waveforms. For example, when generating a combined signal 320, a waveform rerraenting a sinusoidal carrier wave may be generated, and an ultra- wideband pulse may also be generated. Once the waveforms are generated the data symbols are used to modulate, or encode the waveforms, which are represented as numerical values. That is, the encoding of data onto Hie two, or more representations of canmurrication waveforms is performed digitally by dgorithms fliat generate numerical values representmgthenowenccdedcOmmuricationwavefoiiris.
  • step 270 this digital sequence is passed to the digital-to-analog converter (DAQ for conversion to an analog waveform resulting in combined signal 320 that is then transmitted in step 190.
  • DAQ digital-to-analog converter
  • the transmission step 190 may employ one or more antennas, amplifiers and/or filters to lacilitate transmission over the communication channel of interest, and/or other components necessary to accomplish signal Irarismissionatihechosenradio frequency and ihtOughthechosmconimumcaficaimedium
  • tfiese signals may be transmitted through any communication medium, such as air, wire, cable, space, or any other medium.
  • any communication medium such as air, wire, cable, space, or any other medium.
  • multiple communication signals may be generated by the present invention, such as ultra-wideband (UWB) pulses 1hat may be transmitted tfioughpower lines (illustrated as 'XJWB through Power lines"), cable (illustrated as "UWB faough Cable”), and the air (illustrated as 'TJWB Wireless").
  • UWB ultra-wideband
  • the present invention may also generate carrier waves, such as sinusoidal communication signals like 80211 (b/g) and/or 802.11 (a), or other conventional communication signals.
  • An exampleofa combined signal 320 maybe aidt ⁇ -widebandpulseftiatmaybeiiansnittedihoughapower line at afiequencyihat may range from about 5 MHz to about250]Vu44 and simultaneoudy a 8021 l(b/g) signal t ⁇ b ⁇ transmitted at about 2.4 GHz.
  • Hie cxanbined signal 320 maybe passed through two or more band ⁇ pass filters that each may pass the desired signal's frequency (say, 10 MHz for the power line, and 2.4 GHz for the 8Q2.11(b/g)), and filter the unwanted signal
  • the DAC 270 of Hie present invention may generate communication signals up to, andbeyond 10 GHz.
  • UWB wireless pulses may be generated wi1hm1heircunOntFCC-rnat ⁇ latedfiequencybandof3.l GHzfo 10.6 GHz, and a 802. ll(a)signalmaybe generated at 5.4 GHz.
  • the DAC 270 creates an analog waveform from the summed samples.
  • a DAC is an electronic circuit feat converts digital information (for example, Hie digital sequence of summed samples) into analog information, such as a waveform suitable for transmission DACs are ofien characterizedby their "sampling" rate, which is the interval that measurements of a source are taken. IQ the above-described example, the source is the digital sequence of summed samples.
  • an analog waveform may be reconstructed from samples taken, at equal time intervals, but the sampling rate must be equal to, or greater 1han, twice the highest frequency romponent in the analog waveform. That is, if the highest frequency component in an analog waveform is 5 gigahertz (GHz), then the samplingrate must be at least 10 GHz.
  • GHz gigahertz
  • DAC 270 must have a sampling rate of at least 10 GHz to directly generate a 5 GHz radio frequency waveform.
  • a DAC 270 employed by the present invention has a sampling rate of at least 20
  • the DAC 270 includes a novel current switching circuit 1hat assists in oveicoming parasitic capacitance of the circuit elements.
  • DACs generally include Ihousands of transistors.
  • the capacitance of an electronic component is usually not a limitation. Since impedance due to capacitance is a function of frequency, as the speed (i.e., frequency) of a circuit increases, flie influence of capacitance becomes more significant For example, parasitic effects Ihat cause timing delays due to capatitorchaighg can affect ⁇ rOTtr ihmulti-HtDACXihetimmgofcurr ⁇ itsmustbeprecise. Fora fixed capacitance, an increased amount of current can help overcome fliese, and other, parasitic effects.
  • the DAC of the present invention employs arrays of current sources.
  • the current sources are not turned on and off but remain on during the operation of the DAC.
  • the cumerrt sources are switched across aresistive load to form an output voltage
  • Switchched current' DAC architecture uses anumber of current sources.
  • a differential parallel data bus 10 is input into multiplexers 20.
  • the differential parallel data bus 10 receives data for processing by Ihe DAC.
  • the differential parallel data bus 10 can operate at an integer factor of 4 times slower ten tiie DAC because of the 4 to 1 multiplexers 20.
  • the multiplexers 20 iun 4 times faster tiian the differential data bus 10. For example, if flie multiplexers 20 operate at 12 GHz, the differential parallel data bus 10 operates at 3 GHz (1/4 of 12), or if the multiplexers 20 operate at 20 GHz 3 the differential parallel databus 10 operates at 5 GHz(l/4of20).
  • the output from 1he multiplexers 20 is passed to the high-speed differential data bus 30.
  • the high-speed data bus 30 operates at fee same speed as fee multiplexers 20.
  • Current switching network 40 uses 1heMgh-speed data bus 30 to tomidiflkei ⁇ ial analog outputs 50.
  • High speed databus 30 inputs difFerential data intoabank of differential pair transistors 70A-F. One pair of inputs from the high speed data bus 30 is shown in difierential pair transistor 70A.
  • the other differential pair transistors 70B-F obtain data from fee high speed data bus 30 in a similar fashion, but the high speed databus 30 inputs are not shown for clarity.
  • the differential pair transistors 70A-F switch or steer current from current sources 80A-F through load resistors R 1 -R 3 .
  • the high-speed data bus 30 is connected in order from the most significant bit (MSB) to the least significant bit (LSB), then to the differential pair transistors 70A-F that control switching for current sources 80A-F.
  • MSB of the high-speed data bus 30 controls the switching of the differential pair transistor 70A connected to the largest current source 80A, whichis 32 times thecurrent (321).
  • each current source 80A-F which in this embodiment ranges from twice the current (21) to 32 times the current (321), and the parasitic capacitor effects, this precise timing is diffi ⁇ ilttoaco ⁇ nplish To achieve this precise timing, fee LSB current is not halved withrespect to next bit That is, fliecurre ⁇ t source
  • the load resistor Ri is split to provide the current insertion point between load resistor R 2 and load resistor R 3 .
  • This split of load resistor Ri allows the same output voltage to be developed at differential output 50 that would have been developed if the LSB cunenthadbeenIinsteadof2L ByhavingfcedifferentMpair1ransistors70A-FNOT current spread is minimized, Ihereby allowing precise synchronization of state changing for all the differential pair transistors 70A-F.
  • a DAC 270 incorporating the features discussed above may have a sampling rate of at least 20 GHz, thus allowing it to directly generate a 10 GHz radio frequency waveform. It will be appreciated feat fee ernbodimenis of fee present invention relating to direct synthesis of ⁇ mmumcation waveforms at their transmission fiequeaicies is not limited to DACs having 20 GHz sampling rates. As technology progresses, DAC sampling rates will increase, Ihereby allowing direct synthesis of communication waveforms at transmission frequmdesgreaterthan lOGHz.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Transmitters (AREA)
  • Dc Digital Transmission (AREA)

Abstract

L'invention concerne un appareil, des systèmes et des procédés permettant de synthétiser directement et numériquement des signaux ou des formes d'ondes de communication. Les formes d'ondes qui transportent des données sont générées par un convertisseur numérique-analogique (CNA) à la radiofréquence utilisée pour transmettre les formes d'ondes. Dans un mode de réalisation, l'invention concerne un processeur numérique conçu pour coder des données en au moins un symbole de transmission représentatif. Un générateur de formes d'ondes, par exemple un (CNA), est destiné à générer une forme d'onde à partir de symboles de transmission représentatifs. La forme d'onde est alors transmise.
PCT/US2005/028798 2004-09-24 2005-08-11 Synthese numerique de signaux de communication Ceased WO2006036330A2 (fr)

Applications Claiming Priority (2)

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US10/950,056 2004-09-24
US10/950,056 US20060067293A1 (en) 2004-09-24 2004-09-24 Digital synthesis of communication signals

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WO2006036330A2 true WO2006036330A2 (fr) 2006-04-06
WO2006036330A3 WO2006036330A3 (fr) 2007-07-26

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